1 This file contains material useful for client writers.
6 The protocol between Empire client and server is plain text. It is
7 simple enough that you could play using nothing more than telnet.
10 A session uses either ASCII or UTF-8, controlled by session option
11 utf-8. See below for session options. The session always starts in
14 Client-server communication is line-oriented.
16 The server sends lines of output. Each output line starts with an
17 identification string, followed by a space, then arbitrary text, then
20 Identification strings encode small integers called output ids as base
21 36 numbers. Characters '0' to '9' represent digits 0 to 9, and 'a' to
22 'z' represent 10..35, as do 'A' to 'Z'. Symbolic names for ids are
25 empire-client versions before version 4.3.11 parse large output ids
26 incorrectly. Such ids do not currently occur.
28 Clients shall be able to safely handle output lines of arbitrary
29 length. Naturally, a client may not be able to handle a sufficiently
30 large line without loss of functionality, but safety must be ensured.
32 When using ASCII, the most significant bit in text characters
33 indicates highlighting.
35 The following control characters have a defined meaning:
37 ASCII name decimal meaning
38 ----------------------------------------------------
39 horizontal tab 9 move to next tab stop(1)
40 line feed 10 end of line
41 shift out 14 begin highlighting(2)
42 shift in 15 end highlighting(2)
44 (1) Tab stops are every eight columns.
45 (2) Only if session uses UTF-8
47 Other ASCII control characters should not occur and may be ignored by
48 clients. Likewise, overlong or malformed UTF-8 sequences should not
49 occur and may be ignored.
51 The server prompts for input. Each prompt `consumes' one line of
52 input (except for C_EXECUTE, and when a command is aborted, as
53 described below). Input lines are arbitrary text, terminated by line
54 feed, which is optionally preceded by carriage return (decimal 13).
55 Lines should not contain ASCII control characters other than
56 horizontal tab. Clients should not send overlong or malformed UTF-8
59 A client is called synchronous if it waits for a prompt before it
60 sends another line of input. Else it is called asynchronous.
62 Asynchronous clients must take care to avoid blocking on sending
63 input. If the client process blocks that way, it can't receive server
64 output until the server reads more input. That may never happen,
65 because the server may well block on output, which then deadlocks the
68 An Empire session consists of two phases: login and playing.
69 empire-client is synchronous during the former and asynchronous during
70 the latter. Versions before 4.3.11 could deadlock as described above.
75 In the login phase, the server prompts for login commands.
77 The server starts with a C_INIT prompt. The login phase ends when the
78 server sends another C_INIT prompt, which starts the playing phase, or
79 when it closes the connection.
81 The server replies to a login command with another prompt. Except as
82 noted below, the server replies C_BADCMD for syntax errors, C_CMDERR
83 for other errors, and C_CMDOK on success. In any case, the prompt
84 text contains further information intended for humans.
90 Identify the client. This is optional. If given, version
91 information should be included.
95 Set country name to COUNTRY.
99 If another connection is open for this country, forcibly close it,
100 else do nothing. Country must be authenticated.
102 Reply is C_EXIT regardless of success.
104 * options OPTION[=VALUE]...
106 Negotiate session options. Each argument requests setting OPTION to
107 VALUE. The string VALUE is interpreted in an option-specific way.
108 The form without the `=' sets it to an option-specific implied
111 The server accepts the request by sending C_CMDOK. If the server
112 encounters an unknown option, it rejects the request by sending
113 C_BADCMD. It rejects unsupported values by sending C_CMDERR. It
114 may or may not process valid parts of rejected requests.
116 If there are no arguments, the server lists its options. For each
117 option, it sends a C_DATA line with OPTION=VALUE as text, and
118 finally a C_CMDOK. If it supports no options at all, it may reply
119 with C_BADCMD instead.
121 See below for supported session options.
125 Authenticate. Country name must be set already.
127 * play [USER COUNTRY PASSWORD]
131 If no arguments are given, the country must be authenticated
134 Else, argument USER sets the user name, COUNTRY sets the country
135 name, and PASSWORD authenticates.
137 Some error conditions result in a C_EXIT reply. Clients should
138 treat it just like C_CMDERR.
140 On success, the server sends C_INIT. The text is the protocol
141 version number in decimal, currently 2. The client should terminate
142 on protocol versions it doesn't know how to handle.
144 The protocol version is not expected to change often. In fact, it
145 hasn't changed since the oldest known versions of Empire.
147 Unlike the first C_INIT, the second one is not a prompt, i.e the
148 server does not consume a line of input for it.
150 The session then proceeds to the playing phase.
154 Terminate the session. The server replies with C_EXIT and closes
159 List all countries that are still in sanctuary. The output consists
160 of a number of C_DATA lines with human-readable text.
162 This command is only recognized if option BLITZ is enabled.
166 Set the user name. This is optional and defaults to "".
171 In the playing phase, the server sends data, control and prompt lines.
173 Clients signal `EOF' by sending a line "ctld\n", and `interrupt' by
174 sending "aborted\n". The server treats these conditions specially, as
175 described below. Anything else is either a command or input for a
176 command, depending on how the server prompts for the line.
178 empire-client signals `EOF' when it encounters an end-of-file
179 condition while reading player input. It signals `interrupt' when it
180 catches SIGINT, which is normally triggered by Ctrl-C.
182 The following ids occur:
184 * Command prompt C_PROMPT
186 The server consumes a line of input. On EOF, the server terminates
187 the session. Interrupt is ignored. Anything else is interpreted as
190 Text is minutes used, space, BTUs left. Both numbers are in
191 decimal. Clients shall ignore additional text separated by another
194 empire-client prints this prompt using format "[%d:%d] Command : ".
195 Clients with a tty-like user interface are advised to use a similar
196 format, to minimize differences to the examples in info.
198 * Argument prompt C_FLUSH
200 The server consumes a line of input and passes it to the currently
203 The server aborts the command on interrupt and EOF. Any argument
204 prompts it may send before the next command prompt do not consume
205 input. On EOF, the server then terminates the session (but see
206 C_EXECUTE for an exception).
208 If an update runs while the server waits for the line of input to
209 arrive, the current command is aborted. Whether the server consumes
210 a line of input for this argument prompt is unpredictable. Any
211 argument prompts it may send before the next command prompt do not
214 Text is a human-readable prompt supplied by the command.
216 empire-client prints the text verbatim.
220 Text is human-readable server output.
222 empire-client prints the text verbatim.
226 Request execution of a batch file. The text is whatever was on the
227 line of input after the execute command. Its syntax and semantics
228 are left to the client.
230 empire-client interprets the first word (sequence of non-space
231 characters) in the text as file name, and sends the contents of that
234 The security considerations on C_PIPE (below) apply to C_EXECUTE as
237 Note that servers before 4.3.11 sent a copy of the execute command's
238 first argument as text. This made it hard for clients to ensure
239 that the text is identical to what was sent, because the server
240 strips funny characters and interprets and strips '"' characters
241 when splitting input lines into command and arguments.
243 empire-client gets confused when old servers mangle the text that
246 The client shall mark the end of the batch file by signalling EOF as
247 described above. This does not terminate the session. It may
248 signal interrupt if it is unable or unwilling to send the complete
251 While executing the batch file, the server rejects redirections and
252 execute commands, and sends no C_PROMPT command prompts. It still
253 sends C_FLUSH argument prompts.
255 Protocol flaw: not sending C_PROMPT here screws up redirections:
256 they'd apply until the next C_PROMPT, i.e. from start of redirected
257 command until end of containing batch file. That's why the server
258 rejects redirections in batch files.
260 Certain bad failures make the server ignore the rest of the batch
261 file file. This feature is too hard to predict to be really useful.
263 Protocol flaw: strictly asynchronous clients cannot support
264 C_EXECUTE correctly. By the time C_EXECUTE arrives, the client may
265 have sent more input already. That input `overtakes' the contents
266 of the batch file in the input stream, and is interpreted as part of
267 the batch file. Because this is almost certain to happen when the
268 execute comes from a batch file, the server rejects execute commands
271 empire-client has this problem.
273 Clients are not required to support C_EXECUTE. Clients are
274 encouraged to offer alternative means for scripting.
278 End of session. The server is about to close the connection. Text
279 is a human-readable farewell.
281 empire-client prints this text prepended with "Exit: ".
285 Asynchronous message. The client should display the text
288 empire-client prints the text verbatim, prepended by a line feed.
289 This is clearly sub-optimal, because it can be inserted in the
290 middle of user input. Clients wishing to to display asynchronous
291 messages together with normal I/O should insert them before the
294 Although asynchronous messages can be switched off with the toggle
295 command, client support for C_FLASH is not really optional, because
296 a C_FLASH could arrive before the client manages to switch them off.
297 And if the client lets the user send arbitrary commands, the user
298 can switch it back on at any time. A session option controlling
299 C_FLASH would make more sense. Since all popular clients support
300 C_FLASH, it's not worth the trouble.
304 Notification that the number of unread telegrams changed. The text
305 is the notification in human-readable form.
307 empire-client prints the last received C_INFORM text right before
308 each prompt. It also repeats the last prompt when a C_INFORM
309 arrives. This is sub-optimal just like its treatment of C_FLASH.
311 The user can switch these off with the toggle command. Client
312 support is not really optional for the same reasons as for C_FLASH.
316 When a command is redirected to a pipeline, its output is preceded
317 by a C_PIPE line. The text is a copy of the redirection, starting
318 with '|'. Syntax and semantics of the text after the '|' are left
321 empire-client executes text after '|' as shell command, with
322 standard input connected to the Empire command's output.
324 The redirection applies to a single command, i.e. until the next
327 For obvious security reasons, clients supporting pipes shall ensure
328 that the text is identical to whatever was sent to the server. Note
329 that the server recognizes redirection only in command lines, not
330 argument lines. Asynchronous clients cannot distinguish the two.
332 empire-client prepares for redirections being recognized in any
333 line, and copes with only some of them being actually recognized.
337 When a command is redirected to a file, its output is preceded by a
338 C_REDIR line. The text is a copy of the redirection, starting with
339 '>', optionally followed by '>' or '!'. Syntax and semantics of the
340 remaining text are left to the client.
342 empire-client interprets the first word (sequence of non-space
343 characters) in the remaining text as file name, and redirects the
344 command's output to that file. The use of the first word is
345 unfortunate, as it arbitrarily limits the user's choice of file
346 names. If the text starts with '>!', it silently overwrites any
347 existing file, with '>>' it appends to the file, and with just '>'
348 it refuses to overwrite an existing file.
350 The redirection applies to a single command, i.e. until the next
353 The security considerations on C_PIPE apply to C_REDIR as well.
357 Other ids do not occur currently. Clients shall deal gracefully
358 with ids they don't know.
360 empire-client treats unknown ids like C_DATA. Versions before
361 4.3.11 prepend "Aborted\n" to C_ABORT lines, and "Error; " to
362 C_CMDERR and C_BADCMD lines for historical reasons.
368 Session options control client preferences. They are not persistent;
369 each session starts with the same default session options.
371 The only session option so far is utf-8. It controls whether to use
372 ASCII (disabled) or UTF-8 (enabled). Initial value is disabled.
373 Setting it to 0 disables, setting it to 1 enables, and the implied
376 Session options should not be confused with command toggle, which
377 controls player preferences. Clients should leave those accessible to
381 Commands Useful for Clients
382 ===========================
387 A number of commands are available for clients that wish to maintain
388 their own game state. These commands are called dumps.
390 dump - Dump sector information
391 ldump - Dump land unit information
392 lost - Report lost items
393 ndump - Dump nuclear stockpile information
394 pdump - Dump plane information
395 sdump - Dump ship information
397 See the various info pages on these for complete documentation on how
398 they work and how you can use them to help improve your clients.
400 Each of the above commands prints a timestamp, which is a decimal
401 number. This together with the timestamp selector enables you to dump
402 incrementally, i.e. retrieve only what changed since another dump.
403 For instance, if `dump *' printed timestamp 855544597, `dump *
404 ?timestamp>855544596' dumps everything changed since.
406 Note that the condition compares with the timestamp value minus one.
407 That's because timestamps have a noticeable granularity: things may
408 change between a dump and the next timestamp increase.
410 Timestamp values are currently seconds since the epoch, but this might
411 change, and clients are advised not to rely on it.
416 Traditional dumps have a number of shortcomings. They cover only the
417 most important part of the game state (sectors, ships, planes, land
418 units, nukes), but not game configuration, loans, news, and so forth.
419 They are not quite complete even for what they attempt to cover.
420 Finally, their output is harder to parse than necessary.
422 The new `xdump' command is designed to overcome these deficiencies.
423 See doc/xdump for the full story.
426 Advice on parsing human-readable command output
427 ===============================================